Some hydrocarbon reservoirs having hydrocarbon-bearing formations are characterized by one or more incidences of high permeability channels within a formation, which can interfere with effective primary, secondary or enhanced recovery of the hydrocarbons found in lower permeability portions of the formation. High permeability channels can be pre-existing, result from, or can be accentuated by previous production activities. During enhanced oil recovery (EOR), high permeability channels, between injector wells (injectors) and production wells (producers), can cause various EOR drive fronts to bypass virgin oil in less permeable zones and cause early breakthrough of the various drive fronts at one or more of the producers.
One production activity that can result in the formation of high permeability channels is the production of heavy or super-heavy oil from formations or formations containing substantial amounts of sand. Typically, the production of heavy and super-heavy oil can include drilling a vertical or slant well into the formation having high sand content. It was common practice, during primary oil production, to exclude sand from the formation by the use of screens or gravel packs. However, it is now better understood in the heavy oil exploitation industry, that the exclusion of sand during primary oil production is not very economical, having a rate of production of about 0.5-5 m3/day.
Therefore, one technique developed for production of heavy or super-heavy oil includes cold heavy oil production with sand (CHOPS). In CHOPS, sand ingress or influx is initiated and sustained as a mixture of sand and oil throughout primary oil production which results in production rates as high as 15-50 m3/day (Dusseault, Maurice, CHOPS: Cold heavy Oil Production with Sand in the Canadian Heavy Oil Industry, The Alberta Department of Energy, March 2002).
As the mixture of oil and sand is produced from the hydrocarbon-bearing formation, finer sand is evacuated from the formation, allowing larger particles to consolidate within the formation. This creates high permeability channels within the formation which has been a benefit to the improved transport of heavy oil during primary oil production.
After primary oil production, Cyclic Steam Stimulation (CSS) has been used in combination with CHOPS(SPE 138091), with periodic steam injection from an injection well. But CSS is characterized by the flow of steam preferentially through the high permeability channels or wormholes, which can extend to nearby production wells, rendering further CSS ineffective.
These wormholes and other high permeability pathways or channels render ineffective most EOR methods, which rely on drive fluids, such as water, steam, chemical, and/or gas, usually applied as dispersed as possible in a formation along a drive front.
Prior art EOR techniques include the injection of steam into the formation through an injection well for hydrocarbon recovery at a spaced away production well. As a steam front permeates throughout the formation, the heat from the steam lowers the viscosity of the heavy oil and urges the heavy oil into the nearby production wells. However, high permeability channels acts as a channel within the formation and allow the steam drive to bypass residual, virgin cold heavy oil in less permeable portions of the formation, flowing preferentially along the high permeability channels, to break through at a production well, minimizing the effectiveness of the EOR technique.
Extraordinary methods have been proposed for blocking high permeability channels, including a gel-foam system for creating a stable foam in the channels for the duration of the gelation time.
Further, injection of steam in EOR techniques has also been associated with formation damage. Steam is often generated from produced water. Often a majority of produced water is condensed steam that has been originally injected in other recovery processes, some of which being formation water. After removal of co-produced hydrocarbons, the remaining water is purified as produced water. The geothermal effect of injecting produced water for creating steam downhole is poorly understood. However, much literature has been directed to the discussion of formation damage due to fines migration, inorganic scaling, emulsion blockage, asphaltenes and other organic deposition (see Journal of Applied Sciences, 7 (21). pp. 3198-3207. ISSN 1812-5654).
One method in the prior art, downhole or in-situ generation of steam has been the formation or steam at a downhole burner by injecting produced water into the downhole burner. This requires pre-treatment of produced water to prevent solids deposition or scaling in the downhole burner. In-situ created steam for enhanced oil recovery (EOR) is typically formed at the downhole burner using water produced from other production operations. Often, such produced water contain dissolved or suspended solids, produced solids such as sand or slit, and injected fluids and additives that may have been placed in the formation as a result of exploration and production activities (Veil, John A., et al., White Paper Describing Produced Water from Production of Crude Oil, Natural Gas, and Coal Bed Methane, Argonne National Laboratory, January 2004).
Scale deposition or scaling is deemed to be one of the most serious formation problems, understood to be primarily due to the incompatibility of injected steam and connate water. Thus prior art techniques, using produced water, often implemented pre-treatment of the produced water to remove dissolved solids that may cause solid deposition and scaling at the injection well.
However, there is still a need for a methodology for blocking high permeability channels for EOR which combines the benefits of disposal of produced water, and does not introduce new components into the formation.